Riboflavin glucoside is known as one of the metabolites of riboflavin found in urine. It is more soluble in water than riboflavin. The solubility of riboflavin glucoside at 20.degree. C. and 37.degree. C. is 2.2 and 3.5 mg/ml, respectively. In comparison, riboflavin has a solubility of 0.1 and 0.2 mg/ml at these temperatures [see Methods in Enzymology, Academic Press, 18B, 404-417 (1971)].
Riboflavin itself is widely used as an additive in drinks for colouring and/or nutrition, but the drinks become cloudy because of its low solubility in water. Riboflavin-containing solutions for intravenous drop injection also become turbid and tend to block the injection tubes. To solve such solubility problems the more soluble riboflavin glucoside could be used instead of riboflavin to prepare clear drinks and injection solutions.
Riboflavin glucoside was first obtained by Whitby with the acetone-dried powder of rat liver [Biochem. J. 50, 433 (1952)]. Glucosidation of riboflavin occurs when riboflavin is incubated in a solution containing transglucosidase and glucosyl donors such as maltose, dextrin, starch, glycogen and salicin. Transglucosidase has been reported to be widely distributed in animal organs, microorganisms and plants such as rat liver, Aspergillus oryzae, Escherichia coli, Leuconostoc mesenteroides, and cotylendons of pumpkin, Cucurbita pepo, and of sugar beet, Beta vulgaris. However, the productivity of riboflavin glucoside by these enzymatic reaction methods or fermentation in media containing riboflavin and glucosyl donors has been rather low, and its purification procedure too complicated, for practical use [see J. Vitaminology 6, 139-144 (1960) and Methods in Enzymology 18B, 404-417 (1971)].